As for metal-clad laminates suitably used as printed circuit boards for electronic/electrical devices, conventionally known are a double-sided metal-clad laminate with a structure having a metal foil laminated on both the upper and lower surfaces of a polyimide film, and a single-sided metal-clad laminate, which is a flexible laminate with a structure having a metal foil laminated only on om surface.
When the aforementioned single-sided metal-clad laminate is manufactured by a method such as thermocompression bonding (hereinafter may also be referred to as thermal lamination) using a bonding sheet with a structure having a thermoplastic polyimide layer disposed on both the upper and lower surfaces of the core layer (heat-resistant film), the thermoplastic polyimide layer disposed on the side having no laminated metal foil may cause trouble by melting and sticking to a metallic roll or protective film, making it difficult to manufacture a single-sided metal-clad laminate itself. Therefore, a technology is proposed, using a polyimide with a specific structure for the thermoplastic polyimide layer positioned on the side having no metal foil laminated thereon (Patent Literature 1, for example). Also, another technology is proposed, using a release film on the side having no laminated metal foil and further using a protective film at least either on metallic rolls or lamination materials (Patent Literature 2, for example).